G protein-coupled receptors sense an astonishing variety of extracellular molecular signals and trigger complex intracellular and physiological responses. They share a common architecture of seven transmembrane helices connected by a broad range of intra- and extra-cellular loops and terminal domains. Structure determination feasibility of this protein family was demonstrated recently with the first high resolution studies on the human &#946;2 adrenergic, turkey &#946;1 adrenergic, and human adenosine A2A receptors. The Center for Membrane Protein Structure Determination (CMPD) has been created to use a protein family specific platform to determine the high resolution structures of 15-20 representative GPCRs distributed across the phylogenetic tree. Receptor structures are needed at a biologically relevant granularity, for small molecule ligand receptors, peptide and protein receptors, lipid receptors, class B-F receptors, and of receptors in the active and inactive functional states. Each receptor structure will be determined with a set of different pharmacological ligands to define the receptor binding site(s). Solution studies will be conducted with purified receptors bound to different ligands to understand receptor dynamics using hydrogen-deuterium exchange and NMR spectroscopy. In collaboration with the NIH screening center, a library of small molecule probes will be used to analyze each receptor and discover allosteric binding sites using a high throughput thermal stability screen. Through a biologically informed selection of representative receptors, we will maximize the CMPD&#8223;s impact through computational modeling of close homologs and functional studies by external collaborators thereby establishing The PSI GPCR Network. The generated data will be provided to the community in a time frame consistent with the guidelines of the Protein Structure Initiative. Technology access will be achieved through on-site training, workshops, meetings, and publications. Processing access to the CMPD core facility will be provided through a 30% pipeline capacity commitment for the PSI:Biology Network nominated targets. Based on the experience of the CMPD investigators, preference will be for human or eukaryotic membrane proteins to maximally leverage the CMPD capabilities.